1. Field of the Invention
The present invention relates to a semiconductor device having a high electron mobility transistor (HEMT), and a method for manufacturing the same.
2. Description of the Related Art
In recent years, a high speed device using a wide gap semiconductor is attracting attention as a power device for mobile communication. A nitride-system semiconductor represented by gallium nitride (GaN) is a material having a small influence on environment, since it does not include arsenic. Further, the band gap of the nitride-system semiconductor is large as 3 eV or more, and breakdown electric field thereof is 2×106 V/cm, which is larger as compared to that of GaAs. Furthermore, the electron speed of the nitride-system semiconductor is approximately the same as that of GaAs (2×107 cm/s), and a discontinuous portion having a larger band exists at a hetero-interface. Furthermore, in the nitride-system semiconductor, a high two-dimensional electronic concentration (1×1013 cm−2) can be generated by piezoelectric effect. Further, regarding a substrate material, the nitride-system semiconductor can be grown on a sapphire substrate, which can be made large in area and has a small high-frequency loss, or even on an SiC substrate, which has excellent thermal conduction. Thus, the nitride-system semiconductor has many excellent capabilities as a semiconductor material for power devices.
Regarding such a nitride-system semiconductor material, especially an AlGaN/GaN-system high electron mobility transistor (HEMT), research and development thereof as a high-output power device for mobile communication have been accelerated in recent years, and even a device of a scale for outputting 100 W, which has a high-output capability that is ten times more as compared to a conventional GaAs-system power device, is being developed.
However, there is no HEMT of an enhancement type (normally-off operation) that is stable and easy to manufacture.
Prior arts are disclosed in Japanese Patent Application Laid-open No. 2003-100775, Japanese Patent Application Laid-open No. Hei 11-67793, Japanese Patent Application Laid-open No. Hei 10-209177, and Japanese Patent Application Laid-open No. Sho 62-169483.